Particle level indicator

ABSTRACT

An apparatus arranged to indicate the level of particles remaining in a housing. The housing dispenses particles therefrom, and the apparatus senses when the particle level is diminished beneath a preselected level. In this manner, additional particles may be added to the housing when the apparatus indicates that the particles therein are depleted.

United States Patent 1191 1111 3,834,806 Whited- Sept. 10, 1974 PARTICLE LEVEL INDICATOR 3,572,551 5/1971 Gillespie et al. 222/1310. 1 1 1 Invemon Charles Whited, Rochester, 3:233:25; Z133; ifftt'aia'iiiijijiijjiiiiijiiiiii.33323? [73] Assignee: Xerox Corporation, Stamford,

Conn- Primary Examiner-Robert P. Greiner [22] Filed; May 7 1973 Attorney, Agent, or Firm-H. Fleischer; James J.

Ralabate; C. A. Green [21] Appl. N0.: 357,995

521 US. 01. 355/3 on, 118/DIG. 24, 118/637, [57] ABSTRACT 73/290 ZZZ/DIG 1, 222/66 An apparatus arranged to indicate the level of parti- Ilet. cles remaining in a housing The housing dispenses Fleld of Search R, 3 particles therefrom and the apparatus senses when l18/DIG. 24, 637; 15 the particle level is diminished beneath a preselected ZZZ/DIG. 1, 6 73/290v level. In this manner, additional particles may be added to the housing when the apparatus indicates References Clted that the particles therein are depleted.

UNITED STATES PATENTS 3,316,836 5/1967 Epstein 118/637 ux 6 4 D'awmg F'gures PAIENIED SEPI 012m SHEET 1 0F 3 F/G. I

PAIENIEDSEPI H 3.834.806

SHEU 3 OF 3 PARTICLE LEVEL INDICATOR BACKGROUND OF THE INVENTION This invention relates to an electrophotographic printing machine, and more particularly concerns an apparatus for indicating the level of particles within a toner particle storage housing utilized in the development system of the electrophotographic printing machine.

The process of electrostatographic printing comprises electrographic printing and electrophotographic printing. In both of the foregoing processes. an electrostatic latent image corresponding to an original document to be reproduced is recorded on an image bearing member. A viewable record is produced by depositing toner particles on the electrostatic latent image to form a powder image thereof. The foregoing is achieved, in electrophotographic printing, by charging a photoconductive surface to a substantially uniform potential. Thereafter, a light image of the original document is projected onto the charged photoconductive surface. The light image dissipates the charge on the photoconductive surface in the irradiated areas to record an electrostatic latent image thereon. Electrographic printing differs from the electrophotographic printing in that the electrostatic latent image is created without the use of a photoconductive material. That is, electrophotography requires the use of a suitable photoconductor, whereas electrography does not. The electrophotographic process was originally disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.

A viewable record of the electrostatic latent image is achieved by contacting the electrostatic latent image with a developer mix of carrier granules and toner particles. Typically, toner particles are dyed or colored thermoplastic particles which are heat settable, whereas carrier granules are ferromagnetic granules. The toner particles and carrier granules are triboelectrically attracted to one another so that the toner particles adhere to the outer surface of the carrier granules. As the developer mix contacts the electrostatic latent image, the greater attractive force thereof causes the transfer and adherence of the toner particles to the electrostatic latent image. Additional toner particles are added to the developer mix as toner particles are depleted therefrom to maintain uniform image density.

In order to produce an efficient electrostatographic printing machine, it is necessary to conveniently and effectively replenish the toner particles used in the formation of copies. This is achieved by dispensing quantities of toner particles from a toner particle storage housing into the developer mix. However, it is readily apparent that as the toner particles are dispensed-from the storage housing, the supply thereof becomes diminished. Thus, it is advantageous to have an apparatus associated with the storage housing for indicating when the toner particle supply therein has been substantially depleted. In this way, additional toner particles may be added to the storage housing to maintain uniform copy density.

Heretofore, various techniques have been utilized to detect the level of toner particles in the storage housing. For example, a machine operator may lower an indicator rod into the storage housing to determine the quantity of toner particles remaining therein. However, a disadvantage in handling toner particles in this manner is the tendency of the particles, due to their extremely small size, to become airborne when the storage housing is opened by the operator. The airborne toner particles contaminate the surrounding area. and reduce the efficiency of the printing machine as well as dirtying the operator and his clothing.

Another approach is to have a rotatable rod with a planar surface disposed in the storage housing. The rod is disposed along the longitudinal-axis of the storage housing and biased by the toner particles to a position indicating the presence of toner particles in the storage housing. However, when toner particles are depleted, the rod rotates to a position indicating the absence of toner particles. Thus, as the toner particles are depleted from the storage housing, the rod rotates indicating that the toner particles therein are depleted beneath a pre-selected level. However, the foregoing type of apparatus does not appear to operate entirely satisfactorily when the storage housing is oscillated about its longitudinal axis. An apparatus of this type is described in co-pending application Ser. No. 266,936 filed in 1972.

Accordingly, it is a primary object of the present invention to improve the apparatus indicating toner particle quantity in a storage housing thereof.

SUMMARY OF'THE INVENTION Briefly stated and in accordance with the present invention, there is provided an apparatus for indicating particle quantity in a housing utilized for the storage thereof.

In the present instance, this is accomplished by housing means, vibrating means, sensing means, and detecting means. The housing means is adapted to store a supply of particles therein. As the vibrating means moves the housing means, particles are dispensed therefrom. The level of particles remaining in the housing means is measured by the sensing means. This is accomplished by mounting the sensing means for movement in the housing means. Only the particles stored in the housing means above a pre-selected level contact the sensing means. The movement of the sensing means relative to the housing means is measured by the detecting means. When the sensing means is in contact with the particles, it moves in unison with the housing means. Contrawise, when the sensing means is spaced from the particles, it moves relative to the housing means. The movement of the sensing means relative to the housing means is measured by the detecting means, thereby indicating that the particle level is beneath the pre-selected level.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 is a schematic perspective view of an electrophotographic printing machine embodying the features of the present invention;

FIG. 2 is a sectional elevational view of the FIG. 1 printing machine developer unit having a toner particle storage housing therein;

FIG. 3 is a schematic perspective view of the FIG. 2 toner particle storage housing incorporating the present invention therein; and

FIG. 4 is a fragmentary view of the apparatus of the present invention utilized in the FIG. 3 toner particle storage housing.

While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all modifications, alternatives and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION With continued reference to the drawings wherein like reference numerals have been used throughout to designate like elements, FIG. 1 schematically illustrates a multi-color electrophotographic printing machine in which the present invention may be incorporated. The electrophotographic printing machine depictedschematically in FIG. 1 illustrates the various components utilized therein for producing color copies from a colored original document. Although the particle level indicating apparatus of the present invention is particularly well adapted for use in the toner particle storage housing of the electrophotographic printing machine depicted in FIG. 1, it should become evident from the following description that it is equally well suited for use in a wide variety of electrostatographic printing machines and is not necessarily limited to the particular embodiment shown herein.

The printing machine illustrated in FIG. 1 employs an image bearing member including a drum having a photoconductive surface 12 secured to and entrained about the circumferential surface thereof. Drum 10 is mounted rotatably within the machine frame (not shown). One type of suitable photoconductive material is disclosed in U.S. Pat. No. 3,255,377 issued to Sechak in 1972. As drum 10 rotates in the direction of arrow 14, it passes sequentially through a series of processing stations. A drive motor (not shown) rotates drum 10 at a predetermined speed relative to the other machine operating mechanisms. Drum 10 has a timing disc (not shown) mounted on one end thereof. The timing disc is adapted to actuate the machine logic so that the various machine operations are coordinated with the rotation of drum 10. Hence, the machine logic coordinates the sequence of events at the appropriate processing stations in conjunction with the rotation of drum l0.

Initially, drum 10 moves photoconductive surface 12 through charging station A. At charging station A, a corona generating device indicated generally at 16, is disposed in a generally transverse direction extending longitudinally across photoconductive surface 12. Corona generating device 16 is adapted to spray ions onto photoconductive surface 12. This charges photoconductive surface 12 to a relatively high substantially uniform po tential. Preferably, corona generating device 16 is of the type described in U.S. Pat. No. 2,778,946 issued to Mayo in 1957.

After photoconductive surface 12 is charged to a substantially uniform potential, drum 10 rotates to exposure station B. At exposure station B, a color filtered light image of the original document is projected onto the charged photoconductive surface. Exposure station B includes a moving lens system, generally designated by the reference numeral 18, and a color filter mechanism, shown generally at 20. One type of suitable moving lens system is disclosed in U.S. Pat. No. 3,062,108

issued to Mayo in 1962, and a suitable color filter mechanism is described in co-pending application Ser. No. 830,282 filed in 1969. Referring once again to FIG. 1, an original document 22, such as a sheet of paper, book, or the like, is placed face down upon transparent viewing platen 24. Filter mechanism 20, lens 18 and lamp assembly 26 are moved in a timed relation with drum 10 to scan successive incremental areas of original document 22 disposed upon platen 24. This creates a flowing light image of original document 22 which is projected onto photoconductive surface 12. Filter mechanism 20 is adapted to interpose selected color filters into the optical light path. The appropriate color filter operates on the light rays passing through lens 18 to record an electrostatic latent image on photoconductive surface 12 corresponding to a preselected region of the electromagnetic wave spectrum, hereinafter referred to as a single color electrostatic latent image.

After the charged photoconductive surface 12 has been exposed to a filtered light image, drum 10 rotates the single color electrostatic latent image recorded thereon to development station C. Three developer units, generally indicated by the reference numerals 28, 30 and 32, respectively, are disposed at development station C. One of the foregoing developer units, i;e., developer unit 28, will be described hereinafter in greater detail with reference to FIG. 2. However, a suitable development station having a plurality of developer units is disclosed in co-pending application Ser. No. 255,259 filed in 1972. Preferably, the developer units are all of a type referred to generally as magnetic brush developer units. A typical magnetic brush developer unit includes a magnetizable developer mix comprising carrier granules and toner particles therein-The developer mix is continually brought through a directional flux field to form a brush thereof. The electrostatic latent image recorded on photoconductive surface 12 is developed by bringing the brush of developer mix into contact therewith. Each of the respective developer units contain discretely colored toner particles corresponding to the complement of the spectral region of the wave length of light transmitted through filter 20, e.g., a green filtered electrostatic image is rendered visible by depositing green absorbing magenta toner particles thereon, whereas blue and red latent images are developed with yellow and cyan toner particles, respectively.

Drum 10 is next rotatedto transfer station D where the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of final support material 34. Final support material 34 may be, amongst others, a sheet of paper or a sheet of polysulfone thermoplastic material. A transfer roll, shown generally at 36, recirculates support material 34 and is electrically biased to a potential of sufficient magnitude and polarity to attract electrostatically toner particles from the latent image recorded on photoconductive surface 12 to-support material 34. Transfer roll 36 rotates in the direction of arrow 38 in synchronism with drum 10. Preferably, transfer roll 36 and drum 10 are rotated at the same angular velocity. Inasmuch as support material 34 is secured releasably to transfer roll 36, it moves in a recirculating paththerewith. This permits successive toner powder images to be transferred from the electrostatic latent image recorded on photodoncutive surface 12 to support material 34 in superimposed registration with one another. Support material 34 is advanced from a stack 40 disposed on tray 42. Feed roll 44, operatively associated with retard roll 46, advances and separates the uppermost sheet from stack 40 disposed on tray 42. The advancing sheet moves into chute 48 which directs it into the nip between register rolls 50. Thereafter, gripper fingers 52, mounted on transfer roll 36, secure releasably thereon support material 34 for movement in a recirculating path therewith. After a plurality of toner powder im-' ages have been transferred to support material 34, gripper fingers 52 space support material 34 from transfer roll 36. Stripper bar 54 is then interposed between support material 34 and transfer roll 36. Support material 34 is separated from transfer roll 36 and advanced on endless belt conveyor 56 to fixing station E.

At fixing station E, fuser 58 coalesces the multilayered transferred toner powder image to support material 34. One type of suitable fuser is described in U.S. Pat. No. 3,498,592 issued to Moser et al. in 1970. Upon completion of the fixing process, support material 34 is advanced by endless belt conveyors 60 and 62 to catch tray 64 for subsequent removal therefrom by the machine operator.

After the transfer process, residual toner particles remaining on photoconductive surface 12 are cleaned therefrom. The residual toner particles are removed from photoconductive surface 12 as it passes through cleaning station F. At cleaning station F, a cleaning corona generating device (not shown) initially neutralizes the electrostatic charge remaining on photoconductive surface 12 and the toner particles. The neutralized toner particles are then cleaned from photoconductive surface 12 by a rotatably mounted fibrous brush 66. A suitable brush cleaning device is described in U.S. Pat. No. 3,590,412 issued to Gerbasi in 1971. Brush 66 is positioned at cleaning station F and maintained in contact with photoconductive surface 12. Thus, after each successive transfer operation, residual toner particles remaining on photoconductive surface 12 are removed therefrom.

Referring now to FIG. 2, there is shown on developer unit, i.e., developer unit 28, in detail. Developer unit 28 is depicted in a sectional elevational view to indicate more clearly the various components utilized thereon. Only developer unit 28 has been described in detail as developer units 30 and 32 are substantially identical thereto. The developer units are distinguishable from one another by the color of the toner particles contained therein and by the geometrical differences due to the angle of mounting. Developer units 28 may have yellow toner particles therein, unit 30 magenta toner particles, and unit 32 cyan toner particles.

The major components of developer unit 28 are developer housing 68, paddle wheel 70, transport roll 72, developer roll 74 and housing means or a toner particle storage housing, indicated generally at 76. Paddle wheel 70 includes a rotary driven hub member 78 with buckets or scops 80 spaced substantially equally about the periphery thereof. As paddle wheel '70 rotates, developer mix 83 is elevated from the lower region of developer housing 68 to the upper region thereof. In operation, clutch gear 84 meshes with gear 86 secured to paddle wheel 70. Gear 84 rotates in the direction of arrow 88 driving gear 86 in the direction of arrow 90, thereby rotating paddle wheel 70 in the direction of arrow 90. When developer mix 82 reaches the upper region of developer housing 68, it is lifted from paddle wheel buckets to transport roll 72. Alternate buckets of paddle wheel 80 have apertures therein so that the developer mix carried in these areas falls back to the lower regions of developer housing 68. As the developer mix falls to a lower region of developer housing 68, it cascades over shroud 92 which is of a tubular configuration with an aperture 94 in the lower region thereof. Developer mix 82 is recirculated so that the carrier granules thereof are continually agitated to mix with fresh toner particles. This agitation generates a strong triboelectric charge to attract the toner particles to the carrier granules. As developer mix 82, in the paddle wheel buckets approaches transport roll 72, the magnetic field generated by fixed magnets 96 attract developer mix 82 thereto. Transport roll 72 moves developer mix 82 in an upwardly direction. If a surplus of developer mix 82 is furnished, metering blade 98 controls the amount of developer mix 82 carried over the top of transport roll 72. Metering blade 98 shears surplus developer mix 82 from transport roll 72. The surplus developer mix falls in a downwardly direction toward paddle wheel 70.

The developer mix which passes metering blade 98 is carried over transport roll 72 and attracted to developer roll 74 by the magnetic field generated by fixed magnets 100 therein. Developer roll 74 moves developer mix 82 into development zone 102 located between photoconductive surface 12 and developer roll 74. The electrostatic latent image recorded on photoconductive surface 12 is developed by contacting the moving developing mix 82, i.e., the charged areas of photoconductive surface 12 electrostatically attract the toner particles from the carrier granules of developer mix 82. At the exit of development zone 72, the strong magnetic field in the direction generally tangential to developer roll 74 continue to secure thereto residual developer mix and denuded carrier granules, i.e., carrier granules lacking toner particles. Upon passing from the development zone, the residual developer mix and denuded carrier granules enter a region relatively free from magnetic forces and fall from developer roll 74 in a downwardly direction into the lower region of developer housing 68. As the residual developer mix and denuded carrier granules descend, they pass through mixing baffie 104 which directs the flow from the ends toward the center of developer housing 58 to provide mixing in this direction.

Shroud 92 controls the fall of the surplus developer mix and denuded carrier granules so that they mix with the toner particles, rather than simply falling into the lower region of developer housing 68. Furthermore, shroud 92 isolates, from the developer mix, an interior cylindrical enclosure in which toner particle storage housing 76 is located. Toner particle storage housing 76 contains a fresh supply of toner particles 106 which pass through aperture 94 in shroud 92 and into the stream of developer mix 82. Adding toner particles at this location insures that they cannot be carried into development zone 102 without some degree of mixing with the denuded carrier granules. Additional toner particles are added to the developer mix in'order to replace those used in forming toner powder images on the copies. This maintains the concentration of toner particles in the developer mix substantially constant providing substantially uniform image density.

i The apparatus, of the present invention, shown generally at 108, indicates the level of toner particles remaining in toner particle storage housing 76. Oscillation of toner particle storage housing 76 about the longitudinal axis thereof dispenses toner particles therefrom. This is achieved by an oscillator motor (not shown) adapted to vibrate toner particle storage housing 76 substantially about the longitudinal axis thereof.

Turning now to FIG. 3, the detailed structural configuration of toner particle storage housing 76 is shown therein. As shown in FIG. 3, toner particle storage housing 76 includes a tubular member 110 having a supply of toner particles 106 therein corresponding in color to that required by the respective developer unit. Tubular member 110 includes a perforated region 112 therein. When tubular member 110 is stationary, toner particles 106 form a bridge over the holes in perforated region 112 and are not dispensed therethrough. However, when tubular member 110 is oscillated about the longitudinal axis thereof this bridging effect is broken causing toner particles 106 to pass through perforated region 112 and into the lower region of developer housing 74. Preferably, tubular member 110 may be molded from a suitable plastic material with perforated region 112 comprising a plurality of substantially parallel equally spaced slots 114 therein.

Sensing means, indicated generally at 114, has a portion thereof in contact with toner particles 106. Under these circumstances, sensing means 114 oscillates in unison with tubular member 110. Sensing means 114 includes a shaft member 116 mounted pivotably at end portion 118 on end plate 120 of tubular member 110. A generally planar member or plate 122 is mounted on the other end region 124 of shaft 116. When planar member 122 is spaced from the toner particles 106, shaft member 116 oscillates relative to tubular member 110. The movement of planar member 122 relative to tubular member 110 is sensed by detecting means, indicated generally at 126. Detecting means 126 senses the movement of plate member 122 relative to tubular member 110. The detailed structural configuration of detecting means 126 will be described in conjunction with FIG. 4. Circuit means, indicated generally at 128 develop an electrical output signal in response to detecting means 126 indicating that planar member 122 is oscillating relative to tubular member 110.

Turning now to FIG. 4 there is shown the detailed structural configuration of the level indicating apparatus 108 of the present invention. As shown therein, detecting means 126 includes a suitable magnetic sensor or pick-up 130 adapted to sense the movement of planar member 122 relative to tubular member 110. By way of example, a suitable magnetic pick-up 130 is preferably Model No. 340-001 manufactured by Airpax Electronic Company, Fort Lauderdale, Fla. If a sub-miniature magnetic pick-up 130 is required, Model No. 10024 may be suitable.

Magnetic pick-up 130 is mounted in door 121 of developer unit 28. The movement of tubular member 110 and planar member 122, in unison with one another, is detected, as well as the relative movement therebetween. Thus, magnetic pick-up 130 senses the movement of planar member 122 when it contacts toner particles 106. Circuit means 128 is set such that the low level display is not energized when magnetic pick-up 130 senses the movement of planar member 122 in unison with tubular member 110. However, circuit means 128 triggers the low level display when planar member 128 vibrates relative to tubular member 110, i.e., when planar member 128 no longer contacts toner particles 106. This permits tubular member to be discarded when toner particles 106 are depleted beneath the preselected level, while permitting magnetic pick-up 103 to re-used for successive tubular members 110.

Shaft member 116 and planar member 122 are preferably made from a suitable metallic material adapted to cut the lines of flux generated by magnetic pick-up 130. Cutting the lines of flux produced by magnetic pick-up generates an electrical output signal which, in turn, is suitably processed bycircuit-means 128. Circuit means 128 may preferably be a suitable discriminator circuit adapted to produce an electrical output signal when the signal from magnetic pick-up 130 is above a predetermined level. The electrical output signal from discriminator circuit 128 is arranged to actuate suitable display means (not shown) such as a buzzer or light panel indicating that the toner particle level in tubular member 110 is beneath the preselected level. Thereupon, the printing machine may de-activate automatically permitting the operator to replace the empty tubular member 110 with one containing toner particles.

In recapitulation, it is apparent that the apparatus of the present invention is arranged to oscillate with the tubular member when the toner particle level therein is above a pre-selected level. However, the apparatus of the present invention oscillates relative to the tubular member when the toner particle level is beneath the preselected level. The oscillation of the sensing means relative to the tubular member is detected and an electrical output signal developed by the circuit means which, in turn, actuates a suitable display and de energize the printing machine. The display indicates that the toner particle level in the tublar member is beneath the pre-selected level. Hence, the machine operator is advised that the toner particle level is low and that additional toner particles are required in order to produce satisfactory copies within the electrophotographic printing machine. I

It is, therefore, evident that there has been provided in accordance with this invention, an apparatus for detecting the level of toner particles in a toner particle storage housing that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. An electrostatographic printing machine of the type having an electrostatic latent image recorded on an image bearing member and a development system adapted to deposit toner particles from a developer mix onto the electrostatic latent image, wherein the improvement includes: Y

means for housing a supply of toner particles;

means for vibrating said housing means to dispense toner particles therefrom; means for sensing the level of toner particles remaining in said housing means, said sensing means being mounted for movement in said housing means and arranged to engage the toner particles stored therein above a preselected level; and

magnetic means, operatively associated with said housing means, for detecting the movement of said sensing means relative to said housing means, said sensing means being adapted to move relative to said housing means when the toner particles stored therein are beneath a preselected level and said vibrating means moves said housing means to dispense toner particles therefrom.

2. A printing machine as recited in claim 1, further including:

circuit means arranged to produce an electrical signal in response to said detecting means indicating movement of said sensing means relative to said housing means; and

means, responsive to the electrical signal generated by said circuit means, for indicating that the quantity of toner particles remaining in said housing means is beneath the pre-selected level and for deenergizing the printing machine.

3. A printing machine as recited in claim 2, wherein said housing means includes a generally tubular member journaled for oscillatory movement substantially about the longitudinal axis thereof and defining a chamber for storing a quantity of toner particles therein, said tubular member having a perforated region arranged to prevent the passage of toner particles therethrough when said tubular member is stationary member in the region of the other end portion thereof, said planar member moving substantially in unison with said tubular member when contacting the particles stored therein and oscillating relative to said tubular member when spaced from the particles stored therein 6. A printing machine as recited in claim 5, wherein said magnetic detecting means is mounted closely spaced to said tubular member in communication with said planar member so as to detect the oscillation thereof relative to said tubular member for indicating that said planar member is spaced from the toner particles in said tubular member.

generally planar member secured to said shaft 

1. An electrostatographic printing machine of the type having an electrostatic latent image recorded on an image bearing member and a development system adapted to deposit toner particles from a developer mix onto the electrostatic latent image, wherein the improvement includes: means for housing a supply of toner particles; means for vibrating said housing means to dispense toner particles therefrom; means for sensing the level of toner particles remaining in said housing means, said sensing means being mounted for movement in said housing means and arranged to engage the toner particles stored therein above a preselected level; and magnetic means, operatively associated with said housing means, for detecting the movement of said sensing means relative to said housing means, said sensing means being adapted to move relative to said housing means when the toner particles stored therein are beneath a preselected level and said vibrating means moves said housing means to dispense toner particles therefrom.
 2. A printing machine as recited in claim 1, further including: circuit means arranged to produce an electrical signal in response to said detecting means indicating movement of said sensing means relative to said housing means; and means, responsive to the electrical signal generated by said circuit means, for indicating that the quantity of toner particles remaining in said housing means is beneath the pre-selected level and for de-energizing the printing machine.
 3. A printing machine as recited in claim 2, wherein said housing means includes a generally tubular member journaled for oscillatory movement substantially about the longitudinal axis thereof and defining a chamber for storing a quantity of toner particles therein, said tubular member having a perforated region arranged to prevent the passage of toner particles therethrough when said tubular member is stationary while allowing the passage of toner particles therethrough when said tubular member is oscillated.
 4. A printing machine as recited as claim 3, wherein said vibrating means includes a motor adapted to oscillate said tubular member about the longitudinal axis thereof.
 5. A printing machine as recited in claim 4, wherein said sensing means includes: a shaft member having one end portion thereof mounted pivotably in said tubular member, said shaft member extending in a direction substantially normal to the longitudinal axis of said tubular member; and a generally planar member secured to said shaft member in the region of the other end portion thereof, said planar member moving substantially in unison with said tubular member when contacting the particles stored therein and oscillating relative to said tubular member when spaced from the particles stored therein.
 6. A printing machine as recited in claim 5, wherein said magnetic detecting means is mounted closely spaced to said tubular member in communication with said planar member so as to detect the oscillation thereof relative to said tubular member for indicating that said planar member is spaced from the toner particles in said tubular member. 